Recombination in cultured human cells will be examined, using well-characterized temperature-sensitive mutants of adenoviruses. The analysis will involve measuring the frequency of recombination between ts mutants of the same serotype and determining the genetic structure of recombinant genomes, derived from interserotypic crosses. The areas to be examined are: 1. The relationship between recombination and DNA-repair, either in cells deficient in various aspects of host-cell DNA metabolism, or under conditions where the virus or host has been treated with agents known to cause respirable DNA-damage. 2. The involvement of virus-specified functions in virus DNA recombination, in particular the role of the adenovirus-specific DNA-binding protein. 3. The parameters of host-cell mis-match repair using artificial virus DNA heteroduplexes, in an attempt to establish the length of repair tracts and the preferred substrates for mis-match repair enzymes. The data obtained will help to define more clearly the substrates, enzymes and products involved in intramolecular exchange in eukaryotic cell DNA.